The Amp Hour

#222 – An Interview With Bil Herd – Zany Z80 Zygology


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The Amp Hour

Dave Jones & Chris Gammell

Description: An Electronics Radio Show

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#222 – An Interview With Bil Herd – Zany Z80 Zygology

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Welcome C128!

  • Bil grew up in Indiana saying things like “see-ment”. Chris mentioned that a lot of how people say things change depending on location in the states. There was a post on /r/dataisbeautiful about this.
  • He grew up grew up fixing stuff and traded for food/beer. Later he started designing synths while listening to Emerson, Lake and Palmer.
  • After leaving school and wanting to fix TVs, he joined the Army nat’l guard and became a teletype repairman to get around the need for a diploma to take the TV repair class.
  • Bil learned to valuable rules while doing repair:
    • Use your eyes to troubleshoot
    • “Shut up and figure it out”
  • Chuck Peddle designed the 6502. He, Jeri and Bil all did a YouTube call together a few years back:
  • At Bil’s first design job (at the scale company), he had to make their own battery backed RAM.
  • After the scale company, he was hired at West Chester PA. There were 5 chip fabs on Route 30.
  • Bil was told about the gig from Hedly Davis who designed the DRAM for the XBOX.
  • There were early problems with the 40 column displays because of the RAS and CAS (DRAM) timing
  • Commodore was in the space above the MOS fab. They were later convicted of dumping chemicals into the water table.
  • A key component was the VIC (Video Interface Chip). This allowed offloading some of the video processing.
    • 6845 for CRTs
    • 6847 color (but lame)
  • TI994A.
  • Sinclair ZX-Spectrum.
  • Bil made a video about the C116:
  • $49 16K memory based upon making their own chips (almost as much as you had to pay for just the memory by itself).
  • C128 was done 5 months before CES
  • When making the chips, they were 7 layers and about 150,000 transistors on a 1 uM process. The designers used Rubylith to make the lithography masks.
  • There were multiple programming languages for the Commodore: CPM
  • The board layout done on a Panasert/American Universal through hold assembly machines.
  • C128 had a switching regulator which ended up benefiting some of the high draw of CPM cartridges.
  • The z80 clock had to go to 4.9V in 10ns. So Bil made a workaround
  • The stringent nature of FCC certifications meant that Bil couldn’t add any more chips to the board…but could add transistors like above.
  • There was also a need to hold reset, so he designed this circuit:
  • FCC worries about the edge frequencies, because of the high harmonics of a square wave.
  • There was a reflection problem that Bil fixed with a long Red/White wire. You can see it on this high res image of a C128 board.
  • Bil has attended and given talks at the VCF( vintage computer forum) in the past. He also met former guest of the show Alan Wolke there.
  • Magic Voice team (formerly on the Speak and Spell)
  • CPM cartridges.
  • The Commodore LCD was a laptop designed and promoted, but never sold…because Marshall Smith (the CEO) was told not to by the competition.
  • Instead, the Tandy Model 100 (which Dave has done videos about) went on to sell tons of units.
  • After leaving Commodore, Bil went to work at an EMS center
  • There is a movie about Amiga called “Viva Amiga” that is promised to come out soon.
  • A documentary of the last day before Commodore shut down was Dave Haney’s “Death Bed Vigil”
  • Bil believes that Commodore was doomed when Jack Tramiel left.
  • The Commodore name was passed around a bunch, but Bil owns site, which has tons of great info about the era.
  • He also runs a site about designing hardware and teaching people about analog/FPGAs at
  • These days you can see an episode of adafruit’s “Ask An Engineer” There he was introduce to Ben who runs (and works with Hackaday stuff).
  • Bil also has a range of videos over on his own YouTube account.
  • You can also find @BilHerd on Twitter.

2 hours didn’t seem like enough! We hope to have Bil back on soon to talk about his current projects and to catch a few more stories from the golden era of 8 bit computers.


And because we mentioned it, the picture of Bil, courtesy of Wikipedia:

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